02_Physical_Constraints_Paper.pdf

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PHYSICAL CONSTRAINTS ON UNIDENTIFIED AERIAL PHENOMENA
Abraham (Avi) Loeb1 and Sean M. Kirkpatrick2
1Head of the Galileo Project, Astronomy Department, Harvard University
60 Garden Street, Cambridge, MA 02138, USA
2All-domain Anomaly Resolution Office
1010 Defense Pentagon
Washington DC 20301, USA
ABSTRACT
We derive physical constraints on interpretations of “highly maneuverable” Unidentified Aerial Phe-
nomena (UAP) based on standard physics and known forms of matter and radiation. In particular,
we show that the fricti…

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Space Telescope. In contrast, the radar signatures of a meter class object would be detectable with our deep space
radars and space fence, much like IM2 was, out to beyond geosynchronous orbit at an altitude above 36,000 km. Such
objects could also become optically detectable as they get close to Earth, especially if they create a fireball as a result
of their friction with air.
Equipped with a large surface-to-mass ratio of a parachute, technological “dandelion seeds” could slow down in the
Earth’s atmosphere to avoid burnup and then pursue their objectives wherever they land. Current radar…

Constraints on UAP
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light years that span the scale of the Milky Way galaxy. Such autonomous systems could be designed to survive even if
the senders are not able to communicate with them, and deposit probes upon arrival to the target planetary systems.
It is likely that any functional devices embedded in the Earth’s atmosphere are not carrying biological entities because
these would not survive the long journey through interstellar space and its harsh conditions, including bombardment
by energetic cosmic-rays, X-rays and gamma-rays (Hoang et al. 2017, 2018; Hoang & Loeb 2020). Interstellar g…

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et al. 2021). This implies that self-replicating probes could reach ∼1010 habitable planets around Sun-like stars in less
than a billion years. Since most stars formed more than a billion years before the Sun (Madau & Dickinson 2014), it
is possible that other technological civilizations predated ours by the amount of time needed for their devices to reach
Earth.
Here we can use time as another constraint. In the propulsion scheme where an interstellar self-replicating au-
tonomous system is travelling at 10−4c, the above analysis argues that ∼1010 habitable planets around Sun-like stars
cou…

Constraints on UAP
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In addition to the thermal, shock, and associated optical signatures of a high velocity, highly maneuvering object,
there is also an ionization and associated radio frequency signature from such an object moving through the atmosphere.
Studies into supersonic and hypersonic vehicles provide a good basis for comparison. While the ionization density
depends on the altitude, shape, material and velocity of the object in motion, some limits can be derived on when
a signature would be detected, implying a limit to the object’s motion prior to the fireball threshold. In particul…

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Frueh, C., Paul, S. M., & Fiedler, H. 2017, in Advanced
Maui Optical and Space Surveillance (AMOS)
Technologies Conference, ed. S. Ryan, 51
Guillochon, J., & Loeb, A. 2015a, ApJL, 811, L20,
doi: 10.1088/2041-8205/811/2/L20
—. 2015b, ApJ, 806, 124,
doi: 10.1088/0004-637X/806/1/124
Hoang, T., Lazarian, A., Burkhart, B., & Loeb, A. 2017,
ApJ, 837, 5, doi: 10.3847/1538-4357/aa5da6
Hoang, T., & Loeb, A. 2020, ApJL, 899, L23,
doi: 10.3847/2041-8213/abab0c
Hoang, T., Loeb, A., Lazarian, A., & Cho, J. 2018, ApJ,
860, 42, doi: 10.3847/1538-4357/aac3db
Hsu, D. C., Ford, E. B., & Terrien, R. 2020, MNRA…